1. Field of the Invention
The present invention relates to a multilayer wiring substrate including a multilayer body including a laminate of a plurality of insulating layers, and an internal wiring electrode provided in the multilayer body.
2. Description of the Related Art
As shown in FIG. 9, a module 500 including a multilayer wiring substrate 501 has been provided (for example, see Japanese Unexamined Patent Application Publication No. 2008-300482 (Paragraphs [0019] to [0050], FIG. 5, etc.)). FIG. 9 is an illustration showing a module including a multilayer wiring substrate of related art. The module 500 includes the multilayer wiring substrate 501, and a semiconductor element 502 (IC) mounted on a surface of the multilayer wiring substrate 501. The multilayer wiring substrate 501 includes a multilayer body 503 formed by laminating a plurality of insulating layers 503a, internal wiring electrodes 504 provided in the multilayer body 503, and a solder resist 505 provided on each of both surfaces of the multilayer body 503. Also, land electrodes 506, on which a component including the IC 502 is mounted, are provided on a first surface of the multilayer body 503, and connection electrodes 507 for external connection are provided on a second surface. Also, the internal wiring electrodes 504 each include a via conductor 504a and an in-plane conductor 504b provided at each of the insulating layers 503a. The via conductors 504a are connected to each other by the in-plane conductors 504b, and hence the IC 502 mounted on the land electrodes 506 at the first surface of the multilayer body 503 is connected to the connection electrodes 507 provided at the second surface of the multilayer body 503 by the internal wiring electrodes 504.
In recent years, an increase in functionality and a reduction in size of a communication mobile terminal, such as a cellular phone or a mobile information terminal, are promoted, and an increase in functionality and a reduction in size of the module 500 mounted on the communication mobile terminal and having various functions are also demanded. Hence, an increase in functionality and a reduction in size of a specific component, such as the IC 502 mounted on the multilayer wiring substrate 501 included in the module 500, are rapidly promoted, and it is required to mount a specific component, in which the number of pins of its input/output terminal is increased and the pitch of the pins is decreased, on the multilayer wiring substrate 501. Therefore, to meet the increase in the number of the pins and the decrease in the pitch between the pins of the input/output terminal of the specific component mounted on the multilayer wiring substrate 501, it is demanded to decrease the pitch between the land electrodes 506, which are provided on the first surface of the multilayer body 503 and to which the specific component is connected.
However, in the multilayer wiring substrate 501 in the related art, the land electrodes 506 and the via conductors 504a connected to the land electrodes 506 are formed via different processes. Therefore, there is a possibility that a positional shift between the via conductors 504a and the land electrodes 506 formed in the different processes is generated, as a result of which a connection failure occurs due to a processing error or a positional shift in the respective processes. Hence, in the related art, the land electrodes 506 having larger areas than end-surface areas of the via conductors 504a exposed from the first surface of the multilayer body 503 are formed, so that the connection failure between the via conductors 504a and the land electrodes 506 is prevented. However, the decrease in pitch between the land electrodes 506 is disturbed by the increase in area of the land electrodes 506 for ensuring connection reliability between the via conductors 504a and the land electrodes 506.
It could be possible to decrease the pitch between the land electrodes 506 by forming the land electrodes 506 with decreased areas on the first surface of the multilayer body 503. However, in general, a metal film made of, for example, Ni or Au is formed by plating on a plane electrode, such as the land electrode 506 exposed from the surface of the multilayer body 503, in order to prevent oxidation and to increase connectivity to an electrode or the like provided in another component. Accordingly, when the area of the plane electrode such as the land electrode 506 is reduced, there is a problem in which a plating film on the plane electrode is less likely to be formed.